Control circuit for sound recording apparatuses



Feb. 22, 1944.

L. THOMPSON CONTROL CIRCUIT FOR SOUND RECORDING APPARATUS Filed May 2'7, 1941 Patented Feb. 22, 1944 UNITED STATES PATENT OFFICE CONTRGL CIRCUIT FOR SOUND RECORDING APPARATUSES Application May 27, 1941, Serial No. 395,421

(Cl. l79-100.4)

8 Claims.

This invention relates to phonographs and more particularly to a dictating machine for controlling the recording of sound on thin disc records.

One object of the invention is to provide an apparatus of the above nature employing an A. C. motor, and having circuits whereby said motor may be selectively supplied with A. C. current from an A. C. supply line or which may be used with a. D. C. supply line by converting the D. C. current through an inverter.

A further object of this invention is to provide meansfor short circuiting the cutting head of the recording apparatus when the latter is in recording position and while the operator is not dictating in order to minimize or prevent undesired feed back" sounds emanating from said cutting head.

A still further object of this invention is to provide a supplementary harness or cord which may be employed for controlling the dictating machine from a remote point, whenever desired.

A still further object is to provide an improved apparatus of the above-nature which will be relatively inexpensive to manufacture, simple in construction, compact, ornamental in appearance, and very efilcient and durable in use.

With 4these and other objects in. view, which will appear as the description proceeds, there has been illustrated by the accompanying drawing, one form in which the invention may be conveniently embodied in practice.

In the drawing:

Figure 1 is a perspective view of the sound recorder cabinet oi a dlctatlng machine together with s. D. C. inverter box, and an A. C. supply cord apparatus-the units thereof being shown in separated relation. a

Figure 2 is a diagrammatic view o: the circuit connections of the same.

Figure 3 is diagrammatic view showing the circuit connections of the remote control cord or harness and its associated control switch.

The dictating machine of the present invention is provided with an electrical ampliiler which may r operate either on A. C. or D. C. current, but employs a disc record turntable which may be driven only by an A. C. motor. Consequently, to operate the dictating machine on D. C.. it is necessary to convert the current to A. C. for the use oi the motor only. The conversion from D. C. to A. C. is accomplished by a vibrator convertor switch herein designated as an inverter, which is similar to a polarity changer of the conventional type. In order to preserve the life of the inverterf' the switch is located on the D. C.

side thereof so that the inverter-is operating only when the motor is turned on. thus preserving the life oi the contacts.

Moreover, by converting only the current necessary for the A. C. motor. the inverter" will always have the same load, which results in greater durability and longer life of the contacts and vibrator.

The supplementary remote control is preferably made in the form oi a harness," or six-wire cord which may be attached to the recorder whenever desired. by merely inserting it within the power circuit. In other words, one end of the harness will be plugged into the dlctating machine and the other end either into the A. C. supply socket or into the D- C. inverter, as the case may be. In this way. the dictator-'s desk will not be littered up with cords, because the branch remote control circuit is the only additional cord located on his desk. This makes for a simple, convenient, and fool-prooi system.

Referring now to the drawing, wherein like reference numerals designate like parts throughout'the sevegal views. the numeral lil indicates the recorder cabinet of a dictating machine oi' the disc record type, such as was disclosed in my prior patent, No. 2,200,866, issued May 14, 1940, and reissued September 22, 1942, No. Re. 22,183, entitled Apparatus for recording sound on thin discs." At the rear oi the cabinet il). provision is made of a 6-prong plug Il which is adapted to be detachably connected to a corresponding S-aperture socket l2 Joined to wires Il, il, Il, Il. and I1, leading to an inverter Il, or to a similar socket I9. The socket II has six apertures, five of which contain contacts connected to' the two wires 2li and 2 I. as shown in Figure 2, leading to a twoprong` plug 22 adapted to be inserted into an A. C. power line. These live contacts are numbered 28, 2l, 2i, 26, and 21, respectively. Contact 23 is connected with contact 26 while the contact 24 is connected to contact 25 and 21. The -sixth aperture has no contact.

The inverter III which is used only when D. C. power is supplied, contains an extension cord Il having two conductors '2l and III leading to a two-prong plug Il adapted to be inserted into a' D. C. power line, not shown. The wires. 29 and I0 oi therextension cord 2l are connected to the wires i4 and Il, respectively. of the inverter socket l2, so that direct current will be supplied to the prongs I2 and n which lead to the terminais $4 and Ii ofthe switch Si located in the recorder cabinet II. The switch Si is provided with a pair of switch blades 3l and l1 which, when ln closed position, will engage contacts 80 and from which a pair of conductors 40 and 4| pass to the A. C.D. C. ampliner 42.

It will thus be seen, that even when the inverter l0 is employed. a portion or the direct current from the supply line will pass directly to the amplilier 42 located within the recording cabinet i0 without being converted to A. C. current.

The conductor 20 of the inverter is also connected at a point 40 to a conductor 44 leading to a fuse 45 and a choke coil 46, which in turn is connected at a, point 41 to a wire 48. A branch wire 40 leads from a point 50 on the wire 40 to the wire I1 of the inverter socket |2, and said wire |1 includes a condenser 5| intermediate the ends thereof. "."he wire 40 is also connected at the point 52 to a conductor 53 leading to a con- 'denser t4 and then to a wire 6s, from which lead three conductors 56, 51. and 58, respectively (see Figure 2).

The conductor 56 is connected through an inductance 58 to a wire 80 which leads to a crosswire 5| from which depend a pair of contacts 02 and 53. Extending below the wire 40 from the point 52 is a wire 54 including a condenser 55, and said wire 64 leads to a. conductor 6B, which has two connections to the wires 51 and 50, at points 51 and 68, respectively. The wire 00 from a point 58, leads to a wire 10 including an inductance 1| which is connected to a crosswire 12 leading to two contacts 13 and 14 located immediately below and in alinement with the contacts 62, 53. A magnetic reed member 40a, such as iron, lies between the two pairs of contacts 52, 53, and 13. 14, respectively, and has at its outer extremity a contact 15 which is located adjacent a stationary contact 16 which is connected by a conductor 11 to a point 18. from which n conductor 19 leads to a filter circuit containing a resistor 80 and a condenser 0|, the latter being Joined by a conductor B2 to the wire 40a at the point 52. The movable reed 40a is also provided with two intermediate contacts 52a and 00a, which are adapted to engage the contacts 52, 00, and 13, 14, alternately as the reed is vibrated by the solenoid 04 as will be hereafter described.

At the Junction point 10, a solenoid 04 is provided, which is connected by a wire 85 leading to a point 0B intermediate the ends oi a transformer primary coil 01, the latter being connected at its top end to the point 50, and at its bottom end to the point 6B by suitable conductors, as shown in Figure 2. The secondary coil 40 of the transformer is connected to the wire l5. and said coil 0B has three taps 00, 00.

and 0|. The tap 00 is herein shown connected to the wire I0 while the taps 80 and 0i are idle.

The switch Si always feeds one branch of the supply circuit through a two-circuit switch Si containing two separate movable converging upper and lower contact arms 02, 00, respectively, which move together whenthe switch is opened or closed. 'I'he switch Sz which is the double throw type is provided with four contact points I4, 05. Il, and Il, the contact point Il being connected by a conductor It to the contact point, 00 of the switch Si. The contact Misconneittbbyawireiltooneprong |00 of the six-prong plug il. The contact 01 is similarly connected by wire |0| to the wire |02 leading to a prong |00 of said plug Ii.

The A. C. motor |04 is connected by a pair of conductors |05 and |00 to the prongs I 01 and |00 of the six-prong plug II and they are adapted to receive the converted A. C. current from the inverter for driving the motor when the current is supplied from a D. C. power line.

The output from the ampliiler 42 is connected to a pair of wires |00 and H0, which lead to a recording head having a needle ||2 for embossing sound grooves upon a record ||0 supported upon a turntable ||4 driven by the A. C. motor |04.

The switch Si is of the double-pole, singlethrow type and feeds one branch oi' the supply circuit through the switch Si which when in upper closed position with the blade 92 engaging the contact feeds the D. C. current back to the inverter unit through the wire and prong IMI-the wire |1 serving to energize said inverter unit, and causing it to generate A. C. current which then travels along the wire i5, prong |01. and Wire |05, respectively, to the A. C. motor |04. and back to the inverter unit through the wire |06, prong |00, and wire I6, respectively. A microphone |40 is connected to the input terminals |4| and |42 of the amplifier 42.

Operation To operate the machine from a D. C. current supply, when the switch Si is turned on by means of a. hand knob. not shown (convenientiy located on the recorder cabinet I0), the amplifier 42 will first be energized with D. C. The operator will then turn a similar hand knob, not shown, to move the switch S2 from the neutral position shown in Fig. 2 to its upper closed position and energize the inverter i0 which in turn will supply the motor |04 with alternating current.

To operate the machine directly from an A. C. supply line, the two wire cords 20 and 2| will be connected to the A. C. line by the plug 22 and the socket I9, and then attached to the sixprong plug Il.

It will bc clear that in the socket I9, the connection of the terminals 20 and 26 together and the terminals 24, 25, and 21 together permits A. C. current to pass along the prongs 32 and 00 leading to the terminals 04 and 05 to the switch Si from which the A. C. current passes through the wire 00 to the upper blade 02 of the switch Sa. By means ci' this construction. when the switch sa is thrown into its upper closed position, the current will pass along the wire 99 to the plug I0 and thus energize the motor conductors |05 and |00 through the prongs |01 an |00 for' running the motor from the A. C. lin This provides an extremely convenient arrangement for operating the dictating rhachine independent oi the type of supply line, using the A. C. power cord when an A. C. supply line is available, and only using the inverter when the current is supplied by a D. C. power line.

Means' t0 prevent "feed back howling It is a common phenomenon where microphones and loud speakers are employed in. close proximity to each other as in public address systems, and electrically amplied dictating machines, that when the gain or ampliication becomes sumcientiy high and the acoustic coupling between the microphone and the loud speaker is sumciently great, the objectionable phenomenon known as howling or "feed back" r l wm be produced. Tous, 1n s dictum machins,

the recording head itself will operate more or less in a manner oi' a loud speaker, and due to the tact that the microphone is generally 1ocated quite close to the rding head, howling. will frequently be produced even without a great amount oi ampiiiler gain. This howling elect" will be greatly exaggerated if the turntable is stationary. because in this case, not only does .the cutting head itself set up sound vibrations.ln the air but the recording needle which is in contact with the disc record will cause said record, as well as the turntable, to likewise function as a loud speaker diaphragm. When the turntable is rotating, the disc record will have less diaphragm action, and the cutting head will act much less eilectively as a loud speaker. 1

According to applicants invention. the above described undesirable phenomenon has been entirely avoided by providing means to short circuit the cutting head during "stand by" periods when no dictation is taking place, thus doing away with feed back howling, and at the same time, this arrangement permits a much greater amount of amplier gain'to be used.

This has been accomplished by arranging the apparatus so that the two-blade switch sa will periorm the function of starting the motor when the switch Bz is in its upward closed position (with the upper switch blade 92 in contact with the point ll) and of stopping said motor and short-circuitlng the cutting head when said switch Sz is in its lower closed position, at which time the lower switch blade DI will engage the contact point 91- the upper blade 82Y of course being there in open The remote control lharness" illustrated in Figure 3 will now be described. This "harness" consists'of a six-wire extension cord generally indicated by the numeral IIS, containing the six individual wires H6, ii'l, ill, ils, |20, and i2i, each o! which is connected at one end to a sixaperture socket |22, and at its other end to a sixprong receptacle |23 having prongs |24, |26, |20, |21, |20, and |28, respectively. The receptacle |22 serves to receive the socket I8 trom the A. C. power line cord or the socket i2 from the inverter. selectively. according to whether A. C. or D. C. current is being used. In either case. the so'cket |22 will be connected to the six-prong plug which is mounted on the recorder cabinet III.

Ihe receptacle |23 has a branch line control cord |30 consisting or three wires lll, |12, and Ill, leading to a remote control switch I, which is in series with the motor switch Si (see Figure 2) oi' the recorder. and is so constructed that the motor will be started whenever the movable spring-pressed switch contact member |25 is depressed. Assuming that the motor switch 8a is "on," when the remote control switch is released, a spring will move the switch member |38 upwardly away from a contact |31 and cause it to engage a contact ist. The common movable contact member |38 ci' said switch will then short-circuit the cutting head since one side ot the cutting head is connected to said member lll through the wires |32, |20 and other connections as described above.

While there have been disclosed in this specication one form in which the invention may be embodied. it is to be understood'tiiat this form has been shown for the purpose oi' illustration only, and that the invention is not to be limited Ato the specinc disclosures, b ut may be modiiled and embodied in various other forms without departing from its spirit. In short, the invention includes all the modiiications and embodiments coming within the scope o! the following claims.

Having thus fully described the invention, what is claimed as new and for which it is desired tol obtain Letters Patent is:

l. In a phonograph recorder which may operi ate on A. C. or D. C., a cutting head having a needle for forming a sound g'roove on a record.

a motor operable only on A. C. current for rotating said record, a microphone, a vacuum tube ampliiier operable on either A. C. or D. C. for ampliiying the sound energy received by said microphone. means to supply to said ampliner a portion of the current from a D. C. power source, an inverter i'or converting another portion oi said D. C. current to A. C. for operating said driving motor a switch for connecting said source to said ampliiler and another switch for connecting said source with said inverter.

2. In a phonograph recorder which may be operated on either A. C. or D. C., a cutting head having means to produce a sound groove on a rotating record, a motor operable only on A. C. current for driving said record, a microphone, a vacuum tube amplirler operable on either A. C.

or D. C. for amplifying the electrical energy received from said microphone, means to energize said amplifier directly from a source of current. means to selectively supply A. C. from an A. C. source of power or convert to A. C. the current from a D. C. source and supply said converted A. C. current to said A. C. record-driving motor a manually actuated switch ior connecting said source to said ampliiler and a second manually actuated switch for connecting said source to said D. C.A. C. converting means.

3. In a phonograph recorder which may be operated on either A. C. or D. CL, a cutting head having means to produce a sound groove on a rotating record, a motor operable only on4 A. C. current for continuously driving said record, a microphone, a vacuum tube amplifier operable on either A. C. or D. C. for amplifying the elec-l trical energy received from said microphone, means to energize said amplifier directly from a source oi current, means to selectively supply A. C. from an A. C. source of power or convert to A. C. the current from a D. C. source and supply said converted A. C. current to said A. C. record-driving motor, a branch harness comprising a three-wire conductor cord leading from said recorder to a point situated remote therefrom, and a switch for controlling the turning on and oil oi the current supplied to said motor.

4. In a recording apparatus for a dictating machine. an'ampiiiler operable on either A. C. or-

D. C., means responsive to said amplier ifor recording sound vibrations on a rotating sound record, a microphone connected to the input of said ampiler for receiving the dictation to be recordedfa'l motor operable only on A. C. for driving said record continuously, means for connection to a source ot D. C. for directly supplying D. C. to said ampiiner, and inverter means for converting D. C. irom said source to A. C. for operating said A. C. motor and two manuallyoperated switches ior iirstconnecting said source directly to saldlanplier. and then to said inverter for indirectly energizing said motor.

5. In a recording apparatus for a dictating machine. an amplider operable on either A. C. or D. C., means responsive to said ampliner for recording sound vibrations on a rotating disc record, a microphone connected to the input of said ampliiler for receiving the dictation to be recorded. a motor operable only on A. C. i'or driving said disc record continuously, means i'or connection to a source of D. C. for directly supplying D. C. to said amplifier, and inverter means from said source of D. C. for operating said A. C. motor.

6. In a recording apparatus for a dictating machine. an amplier operable on either A. C. or D. C., means responsive to said amplier for recording sound vibrations on a rotating record, a microphone connected to the input of said ampliner for receiving the dictation to be recorded. a motor operable only on A. C. for driving said record continuously, means ior connection to a source of D. C. for directly supplying D. C. tosaid amplifier, and inverter means for converting D. C. from said source to A. C. for operating said A. C. motor.

'7. In a recording apparatus for a dictating machine, a microphone. a D. C. amplier connected to said microphone. a continuously rotating record. an embossing head responsive to. the output of said ampliiier for recording sound grooves on said record, an A. C. motor for rotating said record, an inverter for converting to A. C.. current from a D. C. source or supply. means for utilising the converted A. C. current from said inverter to drive said A. C. motor, and means associawd with said inverter for by-passing a portion of the D. C. current trom said D. C. supply directly to said amplifier without conversion to A. C. whereby said recording apparatus may be selectively operated either on an A. C. current supply or on a D. C. current supply.

B. In a phonographic recordingmpparatus. a movable electrical recording head having means to produce a sound groove on a moving record. a microphone located in close proximity to said -head. an electric motor for driving said record, a vacuum tube ampliiier having its input connected with said microphone and its output connected with said recording head, and a single manually-operated switch operable in one position to substantiallyl simultaneously stop said motor and short-circuit said recordingiead and thus nuiiiiy any feed-back howlingmtendency due to the proximity of said microphone to said recording head, said switch being operable in another position to substantially simultaneously restore said motor and recording head to their i original condition, said switch being capable o! manual operation at the will oi' the operator in either direction at any point in the travel oi' said recording head along said record.

LINCOLN THOMPSON. 

